Back-draft damper for exhaust fan

ABSTRACT

A relatively quiet, back draft damper for an exhaust fan constructed as a casting of a vibration absorbing, synthetic, plastic material including integrally formed pivot pins and a stop and being sufficiently resilient to permit the endwise assembly or removal of the pivot pins from fixed journals.

United States Patent [72] Inventor Robert E. Steiner [56] Referen e Cit d Crev Coeuh UNIT ED STA TES PATENTS I 1 PP M 337-427 969 l.592.84l 7/1926 Ansell 98/[19 1 FM 2.460.538 2/1949 Schneider 1 236/45 [451 El dc C 2.687.687 8/1954 PI'UdhOIL. 1. 98/119 [731 Ass'gnee 3,208,670 9/1965 P116161. 236/45 3.285.155 11/1966 Maltenfort 93/119 Primary Examiner-Meyer Perlin Attorney-Charles E. Markham s4 BACK-DRAFT DAMPER FOR EXHAUST FAN 4 Claims 5 Drawing Figs ABSTRACT: A relatively quiet. back draft damper for an ex- [52] US. Cl .1 98/119. haust fan constructed as a casting of a vibration absorbing, 236/45 synthetic, plastic material including integrally formed pivot [51] Int. Cl. F23l 17/00 pins and a stop and being sufficiently resilient to permit the [50] Field of Search 1. 98/1 [9; endwise assembly or removal of the pivot pins from fixed jour- 236/45 nals.

BACK-DRAFT DAMPER FOR EXHAUST FAN This invention relates to back draft dampers for exhaust fans of the off center, butterfly valve type.

characteristically, the off center pivoted, butterfly valve type, back draft damper at times flutters rapidly against its stop and at other times slams closed against its stop under the widely varying back pressure forces incident to its operation. This presents a highly objectionable noise problem in conventional stamped sheet metal valves, which are usually pivotally mounted in the walls of sheet metal housings. Padding the valve stop dog with soft material reduces the noise considerably, but such padding material usually either compresses or deteriorates. Moreover, rattling of metal pivot pins in their journals lnay still give rise to objectionable noise even though the stop is effectively padded.

An object of this invention is to provide a generally new and improved back draft damper of the off center pivoted, butterfly valve type which is relatively quiet in operation and particularly economical to construct and convenient to assemble.

A further object is to provide an off center pivoted, butterfly valve type, back draft damper having relatively low mass so as to present little resistance to exhaust flow when used in low velocity operation and yet possessing sufficient rigidity for the purpose.

A further object is to provide a particularly low cost, off center pivoted, butterfly valve type, back draft damper constructed as a casting with integrally formed pivot members, and a stop member of material which permits flexing of the valve disc sufficiently to insert the pivot members endwise into fixed journals.

Other objects and advantages will become apparent when reading the following description in connection with the accompanying drawing.

In the Drawing:

FIG. 1 is a front elevational view of an exhaust fan housing having a back draft damper constructed in accordance with the present invention, mounted in the outlet thereof.

FIG. 2 is a cross-sectional view of the exhaust fan and back draft damper taken along line 2-2 of FIG. 1;

FIG. 3 is a bottom plan view of the back draft damper taken along line 3-3 of FIG. 1;

. FIG. 4 is a fragmentary cross-sectional view taken along line 4-4 ofFlG. 3; and

FIG. 5 is a side elevational view of the back draft damper shown alone.

Referring to the drawing, an exhaust fan generally indicated at comprises a sheet metal blower housing 12 and a motor driven fan 14 mounted therein. The housing 12 has an inlet 16 and an outlet 18 including a short tube portion 20 for attaching an air duct thereto.

Pivotally mounted in the outlet 18 is a back draft damper generally indicated at 22. The damper 22 comprises a flat, round disc 24 having a pair of pivot pins 26 projecting from opposite sides thereof and supported on bracket portions 28 formed thereon. The pivot pins 26 are aligned on an axis spaced from a parallel center line through disc 24. The damper further comprises a stop member 30 formed integral with disc 24.

The damper 22 is formed as a casting of suitable, synthetic, thermoplastic material, with the pivot pins and stop member formed integral with the disc. The blower housing 12 is provided with a pair of fixed journals 32 on opposite sides of outlet 18, formed as upstanding eyelets by lancing and forming the sheet metal of the housing wall on opposite sides and adjacent to the outlet 18, see FIGS. 3 and 4. The journals 32 are also aligned on an axis which is spaced from the center line of the outlet 18 the same distance the axis of the pivot pins is spaced from the center line of damper disc 24.

While there are other well known, commercially available,

synthetic, thermoplastic materials suitable for the construction of the draft damper 22 by casting, l have employed polypropylene because of its low cost, lightweight resistance to stress cracking and because it possesses the degree of flexibility with the necessary rigidity required for the purpose. Constructing the back draft damper ofsynthetic thermoplastic material, such as polypropylene, permits the low cost casting of the pivots and stop member integral with the disc and provides a flexibility which permits the endwise assembly of pivot members in fixed journals. Moreover, it also provides a more responsive damper due to its relatively low mass, and a less noisy damper because of the inherent ability ofthe material to damp vibrations. Generally, the synthetic thermoplastic materials suitable for this purpose are considerably lighter in weight than conventional metals which may be used, so that a damper constructed of such material has considerably less mass. As a consequence, they are opened with less force and are therefore less restrictive, and when they are slammed closed by arrant back pressure pulses, the impact force of the stop striking the sheet metal housing; is less. Moreover} due to their molecular structure, such suitable, synthetic, thermoplastic materials inherently damp vibrations. Polypropylene, for example, is in the order of one-tenth the weight of brass, one-eighth the weight of steel, and one-third the weight of aluminum. When an exhaust fan in which the back draft damper is to be used is a low capacity fan, as would be employed in a bathroom or closet, the force required to open the damper, and the noise occasioned by its closing, are important considerations.

I claim:

Claim 1. ln an exhaust fan, a blower housing having an inlet and an opening in a wall thereof forming an outlet, a pair of fixed journals formed in said housing wall on opposite sides of 'said outlet, said journals being axially aligned and spaced off center of the outlet, a back draft damper freely fitting in said outlet, said damper comprising a flat disc having fixed thereon a pair of axially aligned off center pivot members projecting from opposite sides of said damper and entered into said journals, a stop member on said damper in overlapping engagement with a portion of said housing wall adjacent said outlet, and said damper including said pivot members and stop member being constructed of a one-piece nonmetallic, vibration absorbing material and'being sufficiently flexible to permit the endwise entry of said pivot members into said fixed journals.

Claim 2. A back draft damper adapted to be pivotally supported in an exhaust opening formed in the wall of an exhaust fan housing on a pair of fixed journals one on each side of said exhaust opening and upstanding from one side of said wall, the damper comprising a flat disc freely fitting said exhaust opening and having a pair of short, axially aligned, pivot members fixed to one side thereof and extending outward oppositely from the periphery of said disc and adapted to be entered into said journals, a stop member fixed to said disc extending outward from the periphery thereof and adapted to engage said housing, said disc, said pivot members, and said stop member being constructed of a one-piece nonmetallic, vibration absorbing material and said disc having sufficient flexibility to permit the endwise entry of said pivot members into said fixed journals.

3. A back draft damper as set forth in claim 2 in which, said disc, said pivot members, and said stop member are formed integrally as a casting of a synthetic thermoplastic material having sufficient flexibility to permit the bending of said disc required to enter said pivot members endwise into said journals and yet having sufficient rigidity to retain its shape under operating conditions.

4. A back draft damper as set forth in claim 2 in which, said disc, said pivot members, and said stop member are formed as an integral casting of polypropylene resin. 

1. In an exhaust fan, a blower housing having an inlet and an opening in a wall thereof forming an outlet, a pair of fixed journals formed in said housing wall on opposite sides of said outlet, said journals being axially aligned and spaced off center of the outlet, a back draft damper freely fitting in said outlet, said damper comprising a flat disc having fixed thereon a pair of axially aligned off center pivot members projecting from opposite sides of said damper and entered into said journals, a stop member on said damper in overlapping engagement with a portion of said housing wall adjacent said outlet, and said damper including said pivot members and stop member being constructed of a onepiece nonmetallic, vibration absorbing material and being sufficiently flexible to permit the endwise entry of said pivot members into said fixed journals. rClaim
 2. A back draft damper adapted to be pivotally supported in an exhaust opening formed in the wall of an exhaust fan housing on a pair of fixed journals one on each side of said exhaust opening and upstanding from one side of said wall, the damper comprising a flat disc freely fitting said exhaust opening and having a pair of short, axially aligned, pivot members fixed to one side thereof and extending outward oppositely from the periphery of said disc and adapted to be entered into said journals, a stop member fixed to said disc extending outward from the periphery thereof and adapted to engage said housing, said disc, said pivot members, and said stop member being constructed of a one-piece nonmetallic, vibration absorbing material and said disc having sufficient flexibility to permit the endwise entry of said pivot members into said fixed journalS.
 3. A back draft damper as set forth in claim 2 in which, said disc, said pivot members, and said stop member are formed integrally as a casting of a synthetic thermoplastic material having sufficient flexibility to permit the bending of said disc required to enter said pivot members endwise into said journals and yet having sufficient rigidity to retain its shape under operating conditions.
 4. A back draft damper as set forth in claim 2 in which, said disc, said pivot members, and said stop member are formed as an integral casting of polypropylene resin. 